This invention relates to the field of video signal processing. More specifically, it relates to conversion of nonstandard video signals into standard signals for subsequent processing.
One example of video signal conversion is in the area of conversion between two different video standards, such as, the European standard and the U.S. standard, the latter being designated National Television Systems Committee standard (N.T.S.C.). As indicated in the prior art statement accompanying this application, a number of prior references deal with scan conversion for converting between two such standards.
A more recent problem is the conversion of nonstandard signals generated by a variety of electronic devices, such as micro computers, into standard signals for further processing. Thus, for example, there exists today a large number of home or personal computers capable, to various degrees, of generating video signals for display on a television set or monitor. In many cases these devices generate nonstandard video signals chosen for their simplicity or convenience of handling by the computer system. An example of such a device is the Apple II computer manufactured by Apple Computer, Inc.
The Apple II computer generates a noninterlaced video signal having a horizontal scan frequency which is an even harmonic of the color subcarrier. This simplifies handling of the video data by the computer and for many purposes is sufficient. However, this approach prevents standard video equipment from distinguishing between luminance and chrominance information and thus, for example, unsatisfactory results are obtained if an attempt is made to superimpose video data from an Apple computer over video information obtained from a N.T.S.C. source. In particular, the Apple video system effectively pulse-width modulates the chroma information.
It is accordingly an object of the present invention to provide a method and apparatus for correcting or converting nonstandard video signals to the N.T.S.C. video standard to permit subsequent processing.
It is another object of the invention to provide a method and apparatus for recovering or restoring the proper relationship of luminance to horizontal timing and chrominance to the color subcarrier.
It is a further object of the invention to provide a method and apparatus for converting nonstandard video signals to the N.T.S.C. standard so that they may be interfaced to various video devices used in the television industry.
A further object is to provide a means and method for gen-locking a corrected video signal to an external composite video signal on the N.T.S.C. standard.
Another object of the invention is to correct nonstandard video signals to the N.T.S.C. standard to permit graphics and alpha-numerics provided in such nonstandard video signal to be superimposed over an external standard video source.
A further object of the invention is to provide conversion of nonstandard signals to N.T.S.C. standard utilizing a minimum amount of memory and without the need to store a full frame of video signals.
Another object of the invention is to convert a noninterlaced video signal to a 2:1 interlaced signal.
A further object of the invention is to convert the horizontal scan frequency of a nonstandard signal from an even harmonic to an odd harmonic of the color subcarrier whereby the chrominance and luminance information become properly related to horizontal timing and the color subcarrier, respectively.
A further object is to eliminate color fringing usually present in some computer video signals and to add proper pedestal, blanking and sync components to the nonstandard signal.
Other objects and advantages of the invention will be apparent from the remaining portion of the specification.